1. Field of the Invention
This invention relates to a film carrier used for semiconductor devices, etc., and produced according to T.A.B. (Tape Automated Bonding) method.
2. Description of the Related Art
As a mounting method suitable for making recently notably advanced semiconductor devices, highly functional, imparting a high performance thereto and making them thinner and smaller, the above-mentioned T.A.B. method using a film carrier has been noted, and its details have been described, for example, in "Guide to TAB Technique" (author: Kenzo Hatada) published by Industrial Research Association Co., Ltd. on Jan. 25, 1990, etc.
As shown in FIGS. 1(A), 1(B) and 1(C), the film carrier is provided on an insulating layer having definite opening parts consisting of a device hole (f) for fitting a semiconductor chip, outer lead holes (c) for taking out leads (outer leads) for connecting to the outside part of a T.A.B. mounting semiconductor device, etc., with a metal conductor layer wiring pattern consisting of finger-form inner leads (e), protruded into the device hole and for connecting to the semiconductor chip, outer leads (d) for connecting to the outside, inspection pads (b) for inspecting the characteristics of the T.A.B. mounting semiconductor device, etc. In addition, (a) refers to sprocket holes.
As shown in FIGS. 2(A), 2(B) and 2(C), the T.A.B. method is carried out by arranging the semiconductor chip inside the device hole of the film carrier, registering the finger-form inner leads protruded into the inside of the device hole with the projected electrode (k) formed on the semiconductor chip electrode, carrying out I.L.B. (Inner Lead Bonding) for connecting the both according to a process of heat contact bonding or the like, carrying out resin-sealing for protecting the semiconductor chip, separating off the accepted product after inspection along the cut lines (i) by means of punching or the like, and connecting and mounting the outer leads onto a printed wiring sheet or the like by means of soldering, an anisotropic electrically conductive resin, or the like.
In recent years, with high integration and high densification of semiconductor devices, particularly, pin-multiplication and pitch-narrowing of wiring patterns, including finger-form inner leads protruding into the device hole, have been remarkably required.
Any of such metal conductor layer wiring patterns including inner leads have been obtained by treating the metal conductor layer adhered directly or by the medium of an adhesive layer, onto an insulating layer of polyimide resin layer or the like of the film layer body, according to a lithographic technique or an etching technique.
As shown in FIG. 3, the etching of the metal conductor layer at the resist pattern formed according to a lithographic technique is in the form of being broader at the upper part and narrower toward the lower part; hence the cross-section of the metal conductor layer wiring patterns shows a trapezoidal form in which the top part is narrower and the bottom part is broader.
In order to correspond to pitch-narrowing for reducing the distance between the respective wirings, it is necessary to reduce the width of the wirings and also use a thin metal conductor layer for preventing the shortcircuit between the wiring patterns at the bottom part of the wiring patterns.
However, since the wiring patterns at the part adhered directly or by the medium of an adhesive onto the insulating layer are reinforced by the insulating layer, the strength of the patterns raises no problem, but on the other hand, there is raised an inconsistent requirement that a thick metal conductor layer is required for the purpose that the inner leads and the outer leads formed inside the definite opening parts endure the heat and force applied at the time of the above-mentioned I.L.B., at the time of resin sealing and at the time of connecting and mounting onto the printed wiring sheet, thermal stress generated at the time of use of the semiconductor devices, etc. to thereby maintain and improve the strength and prevent the leads from breaking.
As processes for solving the above inconsistency, there are a process of retaining only the metal conductor layer forming the inner lead parts, in a relatively thick manner, and a process of using an alloy of a high strength, as the material constituting the metal conductor layer.
Japanese patent application laid-open No. Hei 2-69,951 discloses a process of relatively thickening only the metal conductor layer forming the inner lead part. According to this process, even when the thickness of the metal conductor layer inside the device hole has been relatively increased, the shortcircuit at the bottom part of the wiring pattern at the time of patterning by means of etching is solved by adjusting the shape by means of soft etching or the like at the subsequent pretreating step of gold- or tin-plating treatment to thereby prevent the shortcircuit, but the following two problems are raised:
The first problem consists in that as a process of ensuring the thickness of the metal conductor layer forming the inner lead part, and reducing the thickness of the metal conductor layer at other parts, it is necessary to carry out a selective etching treatment before or after the patterning, but such a selective etching is so long step and requires a lithographc step which is economically inferior.
The second problem consists in that while it is possible to adjust the shape of the bottom part of the inner leads inside the device hole by means of soft etching which is a pretreatment step of gold- or tin-plating treatment, the bottom part of the joint part of the inner leads outside the device hole is not sufficiently treated so hat prevention of a short-circuit between the wiring patterns remains unsolved.
Further, Japanese patent application laid-open No. Hei 2-82,546 discloses a process of using as a material constituting the metal conductor layer, a calendered copper foil containing 10% or less of impurities and having a thickness of 20 .mu.m or less, but this process raises the following two problems:
The first problem consists in that the calendered foil is different in the percentage of calendering, crystalline structure, etc., between the direction in which the calendering treatment has been applied onto the foil and the direction perpendicular to the above so that various values of physical properties of the foil such as coefficient of thermal expansion, etching characteristics, etc. exhibit directional properties; hence the designs of the film carrier such as arrangement of wiring patterns, etc. are restricted.
The second problem consists in that since the calendered copper foil is produced according to a specific technique of calendering, differently from electrolytic copper foil most used as a metal conductor foil for the film carrier, its production cost is twice or more that of the electrolytic copper foil, and also the alloy foil itself is specific and its cost is higher than those of general foils; hence the above process of using alloy-calendered copper foil is higher in the cost.
The present invention has been made in such a background, and its object is to provide a process for producing a film carrier having a sufficient lead strength, without employing lithographic steps being long, economically inferior and cumbersome, without using an alloy-calendered copper foil accompanied by restriction to the design of the film carrier and higher in cost, and by forming a metal conductor layer of a small thickness causing no shortcircuit between wiring patterns.
In order to achieve the above object, the present inventors have made extensive research in a process for forming a metal conductor layer of a small thickness which avoids a shortcircuit between wiring patterns, while retaining and improving the strength of the wiring leads, particularly inner leads, outer leads, etc. formed inside definite opening parts and without being reinforced by the insulating layer.
As a result, the present inventors have found that when a definite portion of the insulating layer, etc. of the film carrier body is removed by means of a cutting machine to form a definite opening part, and at the same time, a portion of the metal conductor layer as the lower layer of the definite opening part is also removed by cutting to reduce its thickness, then the break strength of the metal conductor layer per unit cross-sectional area is improved.